/*-----------------------------------------------------------------------
 *  MediaFrame is an Open Source streaming media platform in Java 
 *  which provides a fast, easy to implement and extremely small applet 
 *  that enables to view your audio/video content without having 
 *  to rely on external player applications or bulky plug-ins.
 *
 *-----------------------------------------------------------------------
 *
 *  We changed a lot of code and added a lot of functionality.
 *  This includes, but not limited to, the following changes:
 *  1. The project was renamed to MediaFrame;
 *  2. The connection speed detection procedure was added;
 *  3. The JavaScript API functions were added;
 *  4. The pre and post image support functionality was added;
 *  5. The ability to save movie into the local disk was added;
 *  6. The inner buffer for a movie file was added;
 *  7. The click-through functionality was added;    
 *  8. The .zip files support was added;    
 *  9. The realtime feedback agent functionality was added.    
 *  For the full list of the current functionality please visit 
 *  the following web page: http://mediaframe.org/
 *    
 *  06 Jul 2002 - 19 Dec 2004 Konstantin Belous, Oleg Lebedev
 *
 *-----------------------------------------------------------------------
 *
 * 02/12/99 : Java Conversion by E.B , ebsp@iname.com, JavaLayer
 *
 *-----------------------------------------------------------------------
 *  @(#) crc.h 1.5, last edit: 6/15/94 16:55:32
 *  @(#) Copyright (C) 1993, 1994 Tobias Bading (bading@cs.tu-berlin.de)
 *  @(#) Berlin University of Technology
 *
 *  This program is free software; you can redistribute it and/or modify
 *  it under the terms of the GNU General Public License as published by
 *  the Free Software Foundation; either version 2 of the License, or
 *  (at your option) any later version.
 *
 *  This program is distributed in the hope that it will be useful,
 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *  GNU General Public License for more details.
 *
 *  You should have received a copy of the GNU General Public License
 *  along with this program; if not, write to the Free Software
 *  Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
 *-----------------------------------------------------------------------
 */
package mediaframe.mpeg1.audio.decoder;

/**
 * 16-Bit CRC checksum
 */
public final class Crc16
{
    private static	short polynomial=(short)0x8005;
    private		short crc;

    /**
     * Dummy Constructor
     */
    public Crc16() { 
  	crc = (short) 0xFFFF;
    }

    /**
     * Feed a bitstring to the crc calculation (0 < length <= 32).
     */
    public void add_bits (int bitstring, int length) {
  	int bitmask = 1 << (length - 1);
  	do
	    if (((crc & 0x8000) == 0) ^ ((bitstring & bitmask) == 0 )) {
		crc <<= 1;
		crc ^= polynomial;
	    }
	    else
		crc <<= 1;
  	while ((bitmask >>>= 1) != 0);
    }

    /**
     * Return the calculated checksum.
     * Erase it for next calls to add_bits().
     */
    public short checksum() {
	short sum = crc;
	crc = (short) 0xFFFF;
	return sum;
    }
}
